Some medical devices may be implanted within a patient. These implantable medical devices (IMDs) may be implanted at target locations selected to detect a physiological condition of the patient and/or deliver one or more therapies. For example, electrical leads may be delivered to locations within an atria or ventricle to sense intrinsic cardiac signals and deliver pacing or antitachyarrhythmia shock therapy from a stimulation generator coupled to the electrical lead. In other examples, electrical leads may be tunneled to locations adjacent a spinal cord or other nerves for delivering pain therapy from a stimulation generator coupled to the lead. An electrical lead or drug delivery catheter may include a fixation element to secure the distal end of the lead or catheter at the target location.